typeahead.php: An exception catched in typeahead.php has been assigned as array element, instead of a whole array. Fixed.

#3431 / typeAheadSql: columnname 'key' is a reserverd SQL statement - replace by 'id'. Additional the parametername 'typeAheadLdapKeyPrintf' renamed to 'typeAheadLdapIdPrintf'.
typeAhead.php: fixed typo.
TypeAhead.php: introduced new mapping from 'id' (SQL) to 'key' (API).
AbstractBuildForm.php: Constant renamed.
Database.php: update function makeArrayDict() to reflect name mapping.

Typeahead (#3369): Parameternames has changed, configuration is possible on the Form and on the FormElement.
typeahead.php: if there is an exception, the message body is sent as regular 'content' for the dropdownbox. At the moment this is the only way to transmit any error messages.
Ldap.php: missing FE_TYPEAHEAD_LDAP_KEY_PRINTF, FE_TYPEAHEAD_LDAP_VALUE_PRINTF will be substituted by the other. If both missing, an exception is thrown.